Since as early as the 1920s, chain saws have been used to cut wood. Chain saws generally include a power head that drives a saw chain around a guide bar. Chain saws generally come in two configurations: one includes a hand held power head that is handled manually by an operator; and the other includes a power source is part of a machine, such as a harvester, and the operator of the machine controls the cutting operation. The saw chain used for hand held saws and harvesters include a variety of standard and well established pitches.
Saw chain pitch is defined as the distance between any three consecutive rivets divided by two. For the hand held saws, due to power limitations and weight constraints, saw chain pitch has peaked at a maximum pitch of 0.404 inches in modern chain, with the most common pitch being between ¼ and ⅜ inch (e.g. 0.325 inch). Harvesters, on the other hand, have nearly infinite power, and because it is a machine weight is not a significant issue. Further, having a larger pitch, assuming sufficient power is available, increases the speed at which wood may be cut. Thus, Harvester saw chain has generally been held at a minimum of a 0.5 inch pitch, and goes up to and beyond a ¾ inch pitch, with ¾ inch pitch being the most common. While the harvester industry has in the past used a 0.404 inch pitch harvester chain for certain applications, the chassis width on such chains is nearly twice the thickness/width of 0.404 pitch chain used in aggregate or wood cutting operations on hand held saws. The harvester industry is moving away from using chain having a pitch of 0.404 inches, because even with the thicker chassis, such chains have been found to not be durable enough for the power and cutting conditions encountered in harvesters.
Since about the 1960s, it has been known that chain saws may be used for cutting aggregate materials, such as concrete. However, aggregate cutting chain saws were not generally commercialized until the 1990s. The saw chain used for cutting aggregate material differs from that of wood chain primarily in that it uses abrasive blocks instead of cutter links, which results in an abrading operation instead of a true cutting operation. However, for hand held aggregate chain saws, the same power and weight limitations exist, and thus the pitch of aggregate saw chain has been limited to that of the wood cutting saw chain for hand held power units. In order to increase the pitch beyond the 0.404 ceiling, two critical things are needed: first, a larger power head is required to produce more power in order to drive the chain; and second, the components of the chain needed to be scaled up (e.g. thickened) in order to withstand the greater torque encountered by the saw chain. The increased power results in a heavier chain saw, and the scaled up chain components not only results adding overall weight, but it also requires a widening of the kerf width thereby increasing the need for even more power.
For these reasons, just as in the wood cutting saw chain industry, aggregate cutting chain manufacturers have accepted the 0.404 pitch as the ceiling for saw chain used on aggregate cutting chain saws, with ⅜ inch pitch being the current commercially accepted practice. This allows for a chassis that can support a thin enough kerf width such that a lower power output power head may be used and still be sufficient to cut aggregate material. The lower power output power head is necessary to keep the overall weight of the chain saw at or below about 30 pounds, which is a weight deemed generally acceptable by the health and safety practices of the construction tool industry.
Another reason the industry has refrained from going with a larger/longer pitch, is because it presents fewer cutters on a loop of chain to remove material from the work piece. Accordingly, to maintain the same cutting speed each cutter in a longer pitch chain is required to remove more material per pass and thereby experiences increased forces and stress on the chain. Increased pitch typically has required unacceptable increases in features, such as component thicknesses, length, height power requirements, etc. in order to compensate for the increased cutting forces associated with the more aggressive cutters.